A voltage-driven switching element such as an insulated gate bipolar transistor (IGBT) has been used to drive a motor of a vehicle, for example. The switching element is connected to a driving circuit which has a voltage source to apply a drive voltage to the switching element. Further, a control circuit is connected through the driving circuit to the switching element so that a timing of turn-on or turn-off of the switching element can be controlled.
By the way, noise such as overshooting, undershooting, or ringing occurs in the driving voltage to be applied at the switching between ON and OFF of the switching element. When an internal resistance of the drive circuit is increased to reduce the noise, a switching speed at the switching between ON and OFF of the switching element is reduced. As a result, switching loss occurs.
The patent document 1 has proposed a driving device including a driving circuit with a function of changing a rate of change in a driving voltage in order to resolve the trade-off between the noise and the switching loss. This driving element detects the driving voltage and the change rate using multiple detection circuits and feedbacks them to a control circuit. Then, the control circuit outputs a control signal to the driving circuit, thereby changing the driving voltage and its change rate.